1. Field of the Invention
This invention relates to an engine for a model equipped with a fuel injection apparatus and method therefor, and more particularly an engine for a model which is able to throttle fuel sufficiently at the time of low speed revolution to secure the stability of operation and a method therefor.
2. Description of the Prior Art
A carburettor has been conventionally used in a two-stroke cycle or four-stroke cycle globe engine as a means for regulating quantity of fuel supplied to a combustion chamber of the engine.
The present applicant has proposed an engine for a model equipped with a fuel injection apparatus instead of the carburettor. In this engine, air pressure generated in a crankcase is introduced into a combustion tank through a check valve and stored in the tank and fuel is pressurized to 20-100 kPa.
The pressure generated in the crankcase of the engine varies depending on number of revolutions, that is to say, it is high at the time of high speed revolution, and it is low at the time of low speed revolution. Therefore, the aforementioned fuel tank is constructed so that the maximum pressure can be stored therein. It is, however, difficult in practice to maintain stably a constant pressure, for example, at 30-40 kPa.
Therefore, a regulator has been conventionally used in order to control constantly the pressure of fuel supplied from the fuel tank to feed to a fuel injection apparatus. The regulator is an apparatus for passing only the fuel having a certain given pressure.
FIG. 5 is a block diagram of a fuel injection apparatus of a conventional engine for a model and FIG. 6 is a view of timing for the same. A rotatory pulse is generated by a rotatory pulse detecting apparatus mounted to, for example, a crankshaft of an engine. This rotatory pulse is inputted into an injection timing generating circuit 100. The injection timing generating circuit 100 outputs a timing signal which is delayed by time interval t with respect to the rotatory pulse into a fuel injection signal generating circuit 101. An injection period signal proportional to open of a carburettor is inputted into a fuel period generating circuit 102. The fuel period generating circuit 102 generates an actual injection period signal which is inputted into the fuel injection signal generating circuit 101. The fuel injection signal generating circuit 101 generates a fuel injection signal as shown in FIG. 6 which is given to a fuel injection apparatus driving circuit 103. The fuel injection apparatus driving circuit 103 drives a fuel injection apparatus 104 on the basis of the signal.
In a conventional engine of a model which pressurizes the fuel by air pressure in a crankcase and injects the fuel by a fuel injection apparatus, it is premised that the pressure of the fuel is constant, and the supply of the fuel is controlled by injection period. That is to say, when the number of revolutions is low, the injection period is shortened to decrease the quantity of the fuel, and when the number of revolutions is high, the injection period is lengthened to increase the quantity of the fuel.
At the time of low speed, however, the pressure of the fuel rises since the quantity of the fuel used is small, and the fuel becomes dense. And, since the quantity of the fuel used per unit time is large at the time of high speed, the supply of the fuel is not sufficient, and the fuel becomes thin. Therefore, in the conventional engine for a model, the revolution of the engine is unstable and there is possibility in some instances that overheat takes place at the time of high speed and engine stop takes place at the time of low speed.